An object detection apparatus mounted in a system for detecting a target object in various changing environmental conditions. In the apparatus, an acquirer acquires either or both of information indicative of an external environment around the system and information indicative of an operating state of the system. A determiner determines an environmental condition with respect to an input image according to the acquired information. A setter sets, for each of plural image recognition methods each being a combination of one of the plural image recognition dictionaries and one of the plural image recognition techniques, a weighting factor according to the environmental condition determined by the determiner. A detector detects the object in the input image by applying each of the plural image recognition methods to the input image to obtain recognition results reflecting the weighting factors, and collectively evaluating the recognition results.